A. Field of the Invention
The present invention relates to an endoscope having a solid-state image sensing unit inside the distal end of an insertion section, in which a video signal delivered from the image sensing unit is displayed as a picture by a TV monitor, for observation inside the body cavity.
B. Description of the Invention
Conventionally known are endoscopes in which an objective optical system is disposed inside the distal end of an insertion section, which is adapted to be inserted into the body cavity. One or some of lenses of the objective optical system can be moved along the optical axis for focusing, zooming, or change of magnification. One such prior art endoscope is disclosed in U.S. Pat. No. 4,620,769, for example. In this endoscope, a moving lens is controlled remotely from a control section. A coupling mechanism is used to connect a lens frame, holding the moving lens, and a control mechanism in the control section.
Meanwhile, a novel endoscope has recently been developed. In this endoscope, a solid-state image sensing unit is contained in the distal end of its insertion section, and a video signal delivered from the image snesing unit can be displayed as an observation picture by a TV monitor. An example of such an endoscope is stated in Japanese Patent Disclosure (Kokai) No. 58-69528.
In this prior art endoscope, a solid-state image sensing unit and a video processor located outside the endoscope are connected electrically by means of a transmission line, i.e., a shielding line for noise prevention. If a current leaks from the circuit of the image sensing unit, therefore, it flows through a metal shield of the shielding line into a metal member, which constitutes a housing of the distal end of the insertion section. Thus, a patient may possibly receive an electric shock from the leakage current.
Thereupon, an improved endoscope has been proposed to settle such a problem. In this endoscope, an electrical insulating material is used to cover only the outer peripheral surface of a solid-state image sensing unit, thereby securing insulation between the unit and a metallic housing.
In the endoscope constructed so that the moving lens of the objective optical system is moved along the optical axis, for focusing, zooming, or change of magnification of the objective lens, however, a leakage current may possibly flow into the externally exposed housing, through members in contact with the lens frame, holding the moving lens, or through a coupling mechanism connected to the lens frame.